1. Field of the Invention
The present invention relates to image-fixing method and apparatus, image-forming method and apparatus, and toners applicable therefore, all of which are suitably used in an electrophotography, a latent electrostatic recording method, a latent electrostatic printing method, and the like.
2. Description of the Related Art
Conventionally, a heating-roller fixing system has been widely applied as an image-fixing method in multifunctional photocopiers, printers and the like, because of a simple mechanical structure thereof and easy handling.
In the heating-roller fixing system, however, there were drawbacks such that it is necessary to wait until a heating roller reaches at a certain temperature, a thermal capacity of the heating roller has to be large since it is necessary to maintain the temperature of the heating roller at a desirable level in order to inhibit fixing defects and offset phenomena resulted from passages of recording mediums and fluctuation in the temperature of the heating roller due to external factors.
There are also recent trends of the multifunctional photocopiers and printers such that black & white printing has been rapidly taken over by full color printing, and a market for the full color printing is increased.
In the full color printing, a full color toner forms a color by superimposing two or more colors of toners or mixing these colors.
In order to obtain vivid color images with good color reproduction, is it necessary that each color of toners is sufficiently fused and mixed with each other. More vivid color of images can be realized by imparting glossiness.
In order to obtain images without unevenness of glossiness or dot image, it is necessary to employ an elastic layer on a surface of a fixing member as the elastic layer can change its shape depending on a surface configuration of the recording medium at the time of fixing the toner. If the thickness of the elastic layer becomes thicker, however, there are drawbacks such as enlarged thermal capacity, worsen energy-saving, and the like.
Moreover, glossiness of images is related to a smoothness of a surface subjected to fixing. For example, compression from upper side of the fixing surface has been known and employed as means for obtaining smoothness of the surface. In the aforementioned heat-roller fixing system, especially of color printing, a roller having a thick elastic layer is commonly used, and high pressure is applied. The multifunctional full-color photocopier generally utilizes low viscose color toners at a large amount. In such photocopier, the problems arise such that offset occurs or the recording medium wraps around the fixing roller at the time of ejecting due to curvature of the fixing roller. Therefore, it is necessary to apply releasing oil to the roller and to equip an oil tank in the photocopier.
It has been studied to solve the aforementioned drawbacks, and proposed a belt-fixing system and a method which does not apply releasing oil (oil-less system) or a method which applies a small amount of releasing oil. One of the advantages of the belt-fixing system is that a nip is formed by using a thin elastic body which is disposed heating or pressurizing side of the belt. Namely, an elastic member of small thermal capacity can be employed as a belt, and thus this system realizes both a formation of high quality image and energy-saving at the time of fixing.
As a belt-fixing device employing the oil-less system, Japanese Patent Application Laid-Open (JP-A) No. 2003-295664 discloses a fixing device wherein a hardness of a heating roller is adjusted to be higher than a hardness of a pressurizing roller, and the difference of the hardness is defined in terms of Asker C. This fixing device prevents recording mediums from wrapping around the heating roller or pressurizing roller. In the case that full-color image is formed with a large amount of a full-color toner, however, the problems remain such that toner is attached to the fixing belt and offset occurs since oil is not applied for the fixing belt.
Accordingly, it is the current situation that there have not yet been provided an image-fixing method capable of forming high quality images with excellent glossiness while preventing the recording medium from wrapping around the fixing members, and offset occurrence. It is also the situation that there have not yet been provided an image-fixing device, image-forming method, image-forming apparatus, and toner which are suitably applicable for such image-fixing method.
It is therefore an object of the present invention is to provide an image-fixing method which prevents recording mediums from wrapping around fixing members, desirable preventing an occurrence of off-set, providing images with excellent glossiness and high quality. Another object of the present invention is to provide an image-fixing device suitably applicable for the image-fixing method of the present invention, and an image-forming method and an image-forming apparatus utilizing the image-fixing method of the present invention. It is another object of the present invention is to provide a toner suitably applicable for the aforementioned the present invention.